This invention relates to an improved, programmable, process control system of the type which includes a computer, a data memory coupled to the computer, and a program memory which stores a plurality of computer commands.
In the past, relay controls have been used to control processing machines. Recently, two types of programmable control systems for such processing machines have come into use. The first of these types includes freely programmable control systems utilizing digital computers which act to process digital words, each of which is made up of a plurality of bits. The second type includes freely programmable control systems that have no digital computer and which operate as bit processors on individual bits. These types of programmable control systems preferably operate on individual bit data which are fed in, stored, and read out. These individual bit data are used as inputs to logical operations, the result of which determine the manner in which the processing machine is controlled.
The processing speed of control systems which utilize bit processors is often in the range of one micro-second per logical operation. Digital computers of the type used in freely programmable control systems serve mainly for the processing of numerical data and the execution of arithmetic operations. When such digital computers are used to perform logical operations on individual bit data, however, the processing rate is often in the range of 10-20 micro-seconds per logical operation. Because of this slow processing rate, digital computers are on occasion unsuitable for some control systems which require high speed operation.
The slow processing rate of digital computers, when used in a bit processing mode, results from the absence of commands for individual bit processing. For this reason, a digital computer must often execute a series of commands in order to execute a particular desired individual bit operation.